我是一个尝试整合mybatis的新手。终于登上了这个Null Pointer例外。
我的POM
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis-spring</artifactId>
<version>1.1.1</version>
</dependency>
My Spring Config
<bean
class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix">
<value>/pages/</value>
</property>
<property name="suffix">
<value>.jsp</value>
</property>
</bean>
<context:component-scan base-package="biz.canisrigel.slapMe" />
<!-- enable autowire -->
<context:annotation-config />
<bean id="dataSource"
class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost/slapMe" />
<property name="username" value="root" />
<property name="password" value="adminadmin" />
</bean>
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource" />
<property name="typeAliasesPackage" value="biz.canisrigel.slapMe.bean" />
</bean>
<!-- scan for mappers and let them be autowired -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="biz.canisrigel.slapMe.mapper" />
</bean>
我的Mapper
public interface UserMapper {
UserBean getUser();
}
<mapper namespace="biz.canisrigel.slapMe.mapper.UserMapper">
<select id="getUser" resultType="UserBean">
Select * from Users where id = 1;
</select>
</mapper>
用户Bean
只是几个变量
我的DAO
@Service
public class UserDao {
@Autowired
private UserMapper userMapper;
public UserBean getUser(int id) {
if (userMapper == null) {
System.out.println("Errorrrrrr...................");
// return new UserBean();
}
return userMapper.getUser();
}
}
控制器
@Controller
@RequestMapping("/authenticate")
public class LoginController {
@RequestMapping("/index")
public String index() {
UserDao userDao = new UserDao();
System.out.println(userDao.getUser(1).getPassword());
return "Login";
}
}
错误
org.springframework.web.util.NestedServletException:请求处理失败;嵌套异常是java.lang.NullPointerException org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:932) org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:816) javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
答案 0 :(得分:3)
您的UserDao
对象需要来自Spring对象库和映射器。像你一样在你的index
方法中实例化UserDao对象意味着当你打电话时映射器是null
,因为Spring没有为你设置对象,因此无法自动装配你的映射器。
您需要使用@Resource
注释将UserDao对象带入Controller,如下所示:
@Controller
@RequestMapping("/authenticate")
public class LoginController {
@Resource
UserDao userDao;
@RequestMapping("/index")
public String index() {
System.out.println(userDao.getUser(1).getPassword());
return "Login";
}
}